The presence of indoor air particulates is a concern, especially for those people afflicted with breathing or lung disorders such as asthma. These diseases are characterized by an excessive respiratory sensitivity to various stimuli of which a major trigger is particulate matter in household air. Sources of these particulates are varied but a major fraction consists of cigarette smoke, pollen, mold, human/animal dander, feather particles and dust.
As air is circulated through the house via heating, ventilating, and/or air conditioning (HVAC) systems, particulate matter will accumulate inside the system where, especially in cooling systems, they serve as medium for bacteria and fungal growth. The dispersion of microbes such as bacteria, virus, mold, and fungus can be the source of sickness to exposed occupants in the climate controlled area. For example, Legionella pneumophilia has been found to exist in such an environment and has been linked to Legionnaire's Disease. Other microbes can contribute to “sick home” or “sick building” syndrome. Many people are also allergic to the molds and fungus entrained in the dwelling's ventilation as the air passes over contaminated condensate drain water and wet evaporator cooling coils.
The process of reducing indoor air particulates is conventionally accomplished by a filter which permits gases to pass through a porous, typically fiberlike, material that essentially blocks the path and captures the particles before they enter a heating, ventilating, and air conditioning (HVAC) system. Because the pores between fibers are typically larger than the airborne particles the filter relies on the random chance that the particle will become caught on a fiber. If the thickness of the filter is increased or the pores made smaller through the use of a tighter fiber weave, then the resistance to the passage of gases increases thereby increasing the pressure loss, reducing the air flow and ultimately decreasing the system's efficiency.
It is well known that ordinary and widely used, fiber air filters only remove about 20% of particulates when installed. While a denser filter medium would improve filtration, the increased pressure drop across the filter restricts airflow, which in turn causes a decrease in HVAC efficiency and air circulation. These coarse, fiber filters are also ineffective at removing smaller, respirable particles such as smoke particles and pollen, which are a major source of discomfort for people with respiratory conditions such as asthma.
It is also well known to apply a tacky surface to filters to retain particles on the filter's surface. For example, an existing product known as ‘KwikKut™’ made by ‘Precisionaire, Inc.’, is sold on the market as a filter spray for room air conditioners, furnaces, and central air. This product is composed of mineral oil and paraffinic oil for the stated purpose of enhancing filtering in heating, ventilating, and air conditioning systems. Applied to these filters, the spray creates a tacky surface that catches and holds dust, pollen, spores and other airborne contaminants. It can be used on either permanent or disposable filters.
A product known as “Filter Charger” is product offered by Web Products, Inc of Kansas City, Kans. and also uses a scented hydrocarbon spray that remains tacky after being applied by spraying to a filter. This product is formulated by combining a propylene glycol with dielectric properties with morpheline with ionic properties and, thereby negate the dielectric properties of the propylene glycol component.
The use of an adhesive surface to remove particles in the production of semiconductor wafers is disclosed in U.S. Pat. No. 5,753,563.
An alternative method designed for the purpose of increasing particulate removal efficacy without decreasing pore size fiber density is electrostatic attraction. Active electrostatic filters impart a high voltage charge between plates and any charged particles passing through are electrostatically withdrawn from the passing gases and captured on the charged surface (plates). This type of electrostatic system is costly and impractical for residential and small commercial applications because of the maintenance, high voltage, and safety requirements.
To alleviate the need for an applied voltage but still obtain the advantages of electrostatic dust removal, passive electrostatic systems have been developed. A passive electrostatic system relies on dielectric (non-conducting) fibers that harbor electrostatic charges produced from air friction as the air is drawn through the filter. U.S. Pat. No. 5,336,299 discloses an approach in which air passes through dielectric fibers to generate friction that induces a static charge that builds up to a substantial enough quantity to draw out any passing charged particles, namely household dust. This passive electrostatic charge approach is also generally disclosed in U.S. Pat. Nos. 4,702,752; 5,690,719; and 4,944,778 where dielectric fibers are used to capture dust and enhance filter performance. The passive electrostatic filter behaves similarly to active electrostatic filters whereby dust is drawn from the air and adsorbed to the fibers by electrostatic forces without the need for exterior power. Typically because of the cost, this type of passive electrostatic filter is cleaned and reused rather than discarded when dirty.
Moreover, the idea of impregnating a filter with an antimicrobial substance is described in U.S. Pat. No. 5,288,298 where foam filter media is impregnated with an antimicrobial agent, and in U.S. Pat. No. 5,840,245 where inorganic antimicrobial agents are used.